It is a vertebrae but a thoracic vertebrae rather than a caudal. Caudal (tail) vertebrae do not have large dorsal spines. Also on the side you can see the joint surface for a rib. The texture of the bone would suggest a sheep/deer to me rather than a popoise or dolphin.

I am not convinced that this is cetecean and still favour an even toed ungulate. I have attached some photos from the reference collection to try and convince you! The first four are porpoise, the next two juvenile Reindeer and the final four are Roe Deer. All mammals have the crumpled appearance of the vertebral body where the epiphysis and body meet but the epiphyses fuse early in terrestrial mammals and late in cetacea so it is more commonly seen in cetacea, even into adulthood.